The thyroid hormone receptors, encoded by the THRA and THRB genes,
transduce the actions of T3. Receptor expression analysis gave clues on thyroid
hormone and receptor functions in specific brain regions or cell types. This chapter
describes the studies performed on rodents on receptor expression by various
methodologies, including in situ hybridization and the phenotype of Thra and Thrb
knockout mice. Most brain regions express the receptors from fetal stages. Receptor
expression studies on rodents indicate that thyroid hormones regulate neuronal
migration and differentiation during neocortical and cerebellar development. Given the
critical role of thyroid hormones in brain development, it was expected that disruption
of the receptor genes would be equivalent to hormone deprivation. However, in many
cases, this is not so, raising the question of the role of unliganded receptor activity in
hypothyroidism. This chapter ends with the few available data on receptor expression
in the human fetal brain.
Keywords: Aporeceptors, Binding affinity, Cerebellum, Cerebral cortex, Development, Granular layers, Hippocampus, Knockout mice, Purkinje cells, Receptor isoforms, Striatum, Thyroid hormone analogs.
